1. Field of the Invention
The present invention is directed to uninterruptible power supplies and more particularly to a high speed reactive load power snubber circuit for dissipating current transients upon switching of an inverter to transfer alternating current from a load to a storage device of direct current upon the failure of the normal alternating current power line feeding such load.
2. Description of the Prior Art
In today's wide use of computers, data processors, controllers, etc. in data processing systems, it is extremely critical that the system be supplied with continuous power during its operation. Due to inadequate capacity and increasing load demands, commercially-supplied power is often subject to complete failure of the power signals or a reduction in the magnitude of the available voltage during peak demand periods. In cases where various customers subject the power system to sudden electrical loads, transients are generated in the system affecting the magnitude and phase of the supplied power signal.
Since the storage of data in a computer system is predicated on the continuous operation of the computer, power interruptions can adversely affect the integrity of the stored data. When the power drops abruptly, the computer will terminate operation probably with a high possibility of component damage. In order to overcome this situation, computers operating in a data processing system environment have been supplied with uninterruptible power supplies where the primary commercial power source and the reserve power source are connected in parallel. The power supply includes a commercial A.C. line power source and a D.C. voltage energized inverter power source connected in parallel to a switching mechanism which alternately couples one or the other of the two power supplies to the load to be energized. This power supply design provides a substantially uninterruptible power to the load. However, when an inductor load such as a motor is on the line, large current transients are developed upon the starting of the motor. Unless these current transients are dissipated quickly, they can reach a level which can destroy the solid state elements in the power supply. Where the inverter power source is supplying the power, prior power supplies have used silicon controlled rectifiers and large resistor loads to dissipate these current transients. The disadvantage of this type of arrangement is the slow response time of the rectifier in addition to the high cost of the resistor elements.
It is therefore a principal object of this invention to provide a circuit for use in an uninterruptible power supply which will dissipate current transients occurring in an A.C. power signal.
It is another object of this invention to provide a circuit for dissipating a current transient occurring in an A.C. power signal at a high rate of speed.
It is a further object of this invention to provide a circuit for dissipating a current surge in an A.C. power signal for use in an uninterruptible power circuit which is simple in construction and low in cost.